Method for producing stable graphene, graphite and amorphous carbon aqueous dispersions

ABSTRACT

The present patent application relates to a method for producing dispersions and nanodispersions of graphite, graphene and amorphous carbon in aqueous media without using any surfactant and without requiring any chemical modification of the graphene, such as oxidation to produce graphene oxide.

FIELD OF THE INVENTION

The present invention relates a production process of aqueousdispersions of graphene, graphite, nanographite and amorphous carbon,based on the unexpected and unprecedented property of cellulose actingas dispersant of hydrophobic particles in aqueous medium, as agent ofexfoliation of graphite particles and amorphous carbon, spontaneously.This process avoids the use of surfactants in the production of grapheneand the step of transformation of graphite in graphene oxide which isusually necessary to achieve its dispersions in aqueous media.

In this invention, “cellulose” is a polymer registered under CAS Number9004-34-6. The term “cellulose” used here comprises differentcrystalline forms of this polymer, including micro and nanocrystallinecelluloses, and arrangements of macro, micro or nanofibres of differentsizes and aspect ratios.

In this invention, “graphite” comprises and represents the mineralgraphite, with a structure composed of aromatic rings of carbon andregistered under CAS Number 7782-42-5.

In this invention, “amorphous carbon” comprises and represents anysubstances or materials consisting mainly of carbon with thepredominance of conjugated aromatic rings, in particular the compoundsregistered under CAS Number 7440-44-0. It includes amorphous carbonobtained by pyrolysis of wood or other materials of vegetable originwith activation by oxygen and/or acid or alkali compounds, as well asmineral coals and turfs.

BACKGROUND OF INVENTION

To understand the character of novelty of this invention is necessary toknow in detail graphene, graphite and amorphous carbon, theirproperties, the need of their dispersions to be used in differentapplications and also the procedures currently used to disperse grapheneand graphite in water.

Graphite is a material with very unique properties: it is formed solelyof carbon atoms bonded together, forming conjugated aromatic ringsarranged in lamellas that reach macroscopic dimensions, being one of themost known allotropic forms of carbon. It is very nonpolar, hydrophobicand good conductor of electricity and heat. Its acoustic and thermalproperties are highly anisotropic, since the phonons propagate rapidlyalong a plane or lamella, in which atoms are covalently bonded, but notbetween the planes. It has high thermal stability and only oxidizes fastin air at high temperatures, above 700° C. It is diamagnetic, floatingin the air on a magnet. Its properties ensures a large number ofapplications like lubricants, pigments, electrodes, coatings of moldsand brakes, batteries, refractories, anti-flame agents and pressuresensors in microphones and others equipments. It also has undesirableproperties, such as to facilitate corrosion of aluminum and some steels.Moreover, its mechanical properties are very anisotropic, preventing itsuse as a building or structural materials.

Graphene is another allotropic form of carbon, having the structuralbasic unit of graphite, carbon, carbon nanotubes and fullerenes. It isformed of one or a few lamellas of atomic thickness, each formed byhundreds or thousands of conjugated aromatic rings. For this reason,individual graphene lamellae can he understood as a molecule of apolycyclic aromatic hydrocarbon with extremely large number of rings.Its mechanical properties are remarkable, because the graphene sheetsare 207 times stronger than steel per unit mass. It conducts electricityand has important electronic effects: bipolar transistor, ballistictransport of charge and large quantum oscillations.

Amorphous carbons are a large group of substances derived from graphite,but with many chemical and structural defects which produce interestingproperties. The property that gives the highest number applications isthe high adsorption capacity, responsible for the extensive use ofso-called activated carbon in the treatment of water, water effluentsand gases. Other important properties are the mechanical reinforcementand absorption of ultra-violet light, which make the colloidal carbonsor carbon blacks required components of many plastics and rubberarticles, particularly tires used in automotive vehicles.

A large part of the applications of graphite, graphene, amorphous carbonand derived substances, such as carbon nanotubes and fullerenes,requires that they are obtained in dispersions, aqueous or not, ordispersed and mixed with other solids.

For this reason, a great effort of research and development has beendevoted to obtain dispersions and nanodispersions of graphite, graphene,and amorphous carbon, mainly in aqueous media. An evidence of theimportance of this issue is the repercussion of an article describingthe obtainment of graphene in aqueous medium, published by an Australiangroup (Li, D., Muller, M. B.; Gilje, S. Kaner, R. B. and Wallace, G.G.), entitled “Processable aqueous dispersions of graphene nanosheets”and published in Nature Nanotechnology, volume 3, pages 101-105, in2008. This article has been cited more than 4500 times in the scientificliterature, a number that exceeds the total number of citations obtainedby many productive scientists throughout their life. This work hasinspired many patents, for example, the patent application USPTO20130197158, deposited on 2013 Jan. 8, which claims a process ofproduction of nanocomposites of graphene with polyurethanes.

On the other hand, the diversity of applications and the need forconcentrated dispersions of graphene led to the use of exoticdispersants, as the article of Ayan-Varela et al, published in ACSApplied Materials Interfaces, volume 7, pages 10293-10307, 2015, inWhich the authors describe the obtainment of concentrated dispersions(5%) of graphene using as dispersant one flavonucleotide, which is acomplex and expensive substance.

Sang-Soo Lee, Kyunghee Kim, Soon Ho Lim, Min Park, Jun Keung Kim, HeesukKim, Hyunjung Lee; in the U.S. Pat. No. 8,178,201, May 15, 2012, teachtwo methods for obtain graphene from graphite: mechanical delaminationmade by sticking an adhesive tape on graphite and physicochemicaldelamination, described by Sang-Soo and collaborators as: “Such commonmethod for preparing graphene from graphite is roughly separated intotwo types of mechanical and physicochemical delaminations. Themechanical delamination repeats the process of attaching and detachingan adhesive tape on graphite lump to peel graphene off there from. Thephysicochemical delamination comprises the steps of dispersing graphitehaving laminated structure in an appropriate solvent subjecting thegraphite in solvent to oxidation reaction to extend the space betweenthe laminates of the graphite, and, thus to obtain the graphene oxide;and subjecting the graphene oxide to reduction reaction to obtaingraphene.”

The present invention describes a surprising fact, which is theefficient action of microcrystalline cellulose as exfoliating agent,dispersing and stabilizing of graphite, graphene and substances relatedto these, such as amorphous carbon. This result is unexpected becausethe cellulose is not recognized as surfactant or used as dispersant ofpowder particles in aqueous media and is itself well-known for itsinsolubility in any common liquids. On the other hand, dispersants areamphiphilic substance and cellulose is not recognized as amphiphilic bymost researchers, engineers and technicians, although thischaracteristic of cellulose is supported by some research groups in theworld. The results of this present invention are even more surprisingbecause it does not depend on of the oxidation steps of carboncompounds, forming graphene lamellas, which in the current state of theart are necessarily followed by a step of reduction and stabilizationwith surfactants. The formation of the graphene oxide and its reductionforming graphene again are steps that introduce chemical and structuralimperfections in the resultant products, which damage their useproperties.

SUMMARY OF THE INVENTION

The present invention relates to a novel process to produce aqueousdispersions of graphene stabilized by cellulose, offering a newalternative to the current methods of dispersion of graphene. Theprocess which is the object of this invention has the followingadvantages: a) it uses cellulose as dispersant that is biodegradable,renewable, recyclable, nontoxic and compatible with the environment andit is often used in industrial process in alkaline median and even inthe absence of alkali; b) the graphene stabilized with cellulose inalkaline medium becomes unstable when in contact with natural waters,precipitating and therefore being easily removed or concentrated; c) insome implementations of this invention, the graphene dispersed incellulose in alkaline medium has high adhesion to various solidsubstrates, especially cellulosic materials such as textile fibers andpapers, what is desirable in applications in printed electroniccircuits, in other words, electronic/photonic devices mounted on paperor fabrics; d) this process does not requires any chemical modificationor oxidation of graphite or graphene, which is part of the state of artbut presents the disadvantage of destroy partially the graphenestructure, damaging its conductive and optical properties; e) in someimplementations of this invention, the solids obtained by drying of thedispersions, once dried, can be redispersed in aqueous alkalinesolution; f) even when alkaline dispersions are used, the films obtainedby drying are dispersions only mildly alkaline or neutral, because thealkali used in the forming of the dispersion is neutralized byatmospheric CO₂.

The invention also contemplates the products obtained with thesedispersions, such as: conductive inks, conductive adhesives or otherproducts obtained with dispersions of graphene and nanographitestabilized by cellulose.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a photographic image that shows aqueous dispersions containingdifferent concentrations of graphite, cellulose and NaOH, after 24 hoursof decantation. The concentrations (w/w) of each dispersion are: 1) 1%NaOH, 2% cellulose and 2% graphite; 2) 1% NaOH, 2% cellulose and 5%graphite; 3) 1% NaOH, 5% cellulose and 2% graphite; 4) 1% NaOH, 5%cellulose, 5% graphite; 5) 7% NaOH, 2% cellulose and 2% graphite; 6) 7%NaOH, 2% cellulose and 5% graphite; 7) 7% NaOH, 5% cellulose, and 2%graphite; 8) 7% NaOH, 5% cellulose, 5% graphite; 9) 0% NaOH, 5%cellulose 5% graphite; 10) 0% NaOH, 0% cellulose and 5% graphite; 11) 7%NaOH, 0% cellulose and 5% graphite; 12) 0% NaOH, 0% cellulose and 5%graphite.

FIGS. 2A and 2B show images of transmission electron microscopy of adispersion containing 7% NaOH, 5% cellulose and 5% graphite. The imageswere obtained from the same experiment, where the FIG. 2B was acquiredusing a 25 eV energy filter for better distinction of the areas ofcellulose and graphite.

FIG. 3 shows shear stress versus shear rate curves of different mixturescontaining cellulose, sodium hydroxide and graphite. The shear stress ofthe cellulose solution in a concentration of 2% by weight varieslinearly with the shear rate, even in the presence of graphite. However,the addition of graphite in an alkaline solution with 5% cellulosecauses a sharp increase in viscosity, which is an evidence of graphiteexfoliating in lamellar structures containing few sheets.

FIG. 4 is a photographic image of aqueous dispersions containingdifferent concentrations of amorphous carbon, cellulose and NaOH, after24 hours of decantation. The concentrations by weight of each dispersionare: 1) 1% NaOH, 2% cellulose and 2% coal; 2) 1% NaOH, 2% cellulose and5% carbon; 3) 1% NaOH, 5% cellulose and 2% coal; 4) 1% NaOH, 5%cellulose and 5% carbon; 5) 7% NaOH, 2% cellulose and 2% coal; 6) 7%NaOH, 2% cellulose and 5% carbon; 7) 7% NaOH, 5% cellulose and 2% coal;8) 7% NaOH, 5% cellulose and 5% carbon; 9) 0% NaOH, 5% cellulose and 5%coal; 10) 0% NaOH, 0% cellulose and 5% carbon; 11) 7% NaOH, 0% celluloseand 5% coal; 12) 0% NaOH, 0% cellulose and 5% coal.

FIG. 5 is a descriptive flowchart of the method shown in Example 1.

DETAILED DESCRIPTION OF FIGURES

FIG. 1 is a photographic image that shows aqueous dispersions containingdifferent concentrations of graphite, cellulose and NaOH, after 24 hoursof decantation. The concentrations (w/w) of each dispersion are: 1) 1%NaOH, 2% cellulose and 2% graphite; 2) 1% NaOH, 2% cellulose and 5%graphite; 3) 1% NaOH, 5% cellulose and 2% graphite; 4) 1% NaOH, 5%cellulose, 5% graphite; 5) 7% NaOH, 2% cellulose and 2% graphite; 6) 7%NaOH, 2% cellulose and 5% graphite; 7) 7% NaOH, 5% cellulose and 2%graphite; 8) 7% NaOH, 5% cellulose, 5% graphite; 9) 0% NaOH, 5%cellulose, 5% graphite; 10) 0% NaOH, 0% cellulose and 5% graphite; 11)7% NaOH, 0% cellulose and 5% graphite; 12) 0% NAM, 0% cellulose and 5%graphite.

For the preparation of mixtures 1 to 8 solutions and alkalinedispersions of cellulose were initially prepared. First, the sodiumhydroxide was solubilized in water and the solution was cooled to 0° C.,using an ice bath. The cellulose was added to the NaOH solution and themixture was homogenized in a disperser at 6500 rpm for 5 min at 0° C.The mixture was kept at −20° C. in a freezer for 2 h. After thepreparation of cellulose solutions and dispersions, the samples 1 to 8received additions of graphite resulting in the concentrations listedabove. The mixtures 9 to 12 were prepared by additions of the componentsin the water. All mixtures were made in plastic centrifuge tubes withlid and the mixtures were shaken on a reciprocal motion shaker at 360oscillations per minute with a displacement of 2 cm, during 15 h. Themixtures have remained static for 24 h at room temperature (24° C) andwere photographed after the period of decantation.

The mixtures 9 and 10 show that graphite is not dispersed in waterwithout the presence of cellulose, and most of the material remained incontact with the hydrophobic wall of the vial.

In contrast, the system 3 shows total sedimentation of the solids,forming a clear supernatant. The absence of graphite on the wall of theplastic bottle shows that the graphite becomes hydrophilic due tocontact with the cellulose. In addition, macroscopic separation of theconstituents, cellulose and graphite, in the sediments has not occurreddespite the difference of density between them, showing their chemicalcompatibility.

Mixtures 7 and 8 show dispersions which remained stable after 24 hours,wherein the solids remain in suspension, without the formation ofmacroscopic domains of each species. These systems show that thecellulose is a dispersant of graphite in water.

FIGS. 2A and 2B show images of transmission electron microscopy of adispersion containing 7% NaOH, 5% cellulose and 5% graphite. For thesample preparation, the dispersion of cellulose and graphite was dilutedwith water and applied immediately on the specimen holder. The imageswere obtained at 80 kV and in the same region, and the FIG. 2B wasobtained using a 25 eV energy filter for better distinction of the areasof cellulose and graphite. In the images it was possible to check thecontact, at the microscopic level, of cellulose films with the graphitesheets. The chemical compatibility between the two species is visibleand no segregation of the components was observed.

FIG. 3 shows data about the rheological behavior of different mixturesof cellulose, sodium hydroxide and graphite. The graph in this figureshows that the shear stress varies linearly with shear rate in thecellulose solutions with a concentration of 2%, with or withoutgraphite. However, the viscosity of the solution with 5% cellulosedecreases with the shear rate, which is a characteristic property ofnon-Newtonian fluids. Therefore the concentration of 5% by weight ofcellulose is equal or greater than its critical concentration. Theaddition of graphite in an alkaline solution containing 5% cellulosecauses a sharp increase of viscosity, represented by the increase of theslope of the shear stress versus shear rate curves. The viscosityincrease due to the addition of particles is an evidence of theexfoliation of the graphite in lamellar structures containing a fewsheets, as nanographite or graphene. This type of dispersion has reducedits viscosity with increasing shear rate due to the alignment of thenanographite and graphene lamellas in the flow direction, facilitatingthe movement of the fluid. For shear rates employed in this rheologicalanalysis, dispersions containing 2% graphite show very high viscosity,reaching 40,000 cP, and dispersions containing 5% graphite presentaspect of slurries, with viscosity up to 176000 cP.

FIG. 4 is a photographic image of 12 aqueousdispersions containingdifferent concentrations of commercial activated carbon, cellulose andNaOH, after 24 hours of decantation. The concentrations by weight ofeach dispersion are: 1) 1% NaOH, 2% cellulose and 2% activated carbon;2) 1% NaOH, 2% cellulose and 5% activated carbon; 3) 1% NaOH, 5%cellulose and 2% activated carbon; 4) 1% NaOH, 5% cellulose and 5%activated carbon; 5) 7% NaOH, 2% cellulose and 2% activated carbon; 6)7% NaOH, 2% cellulose and 5% activated carbon; 7) 7% NaOH, 5% celluloseand 2% activated carbon; 8) 7% NaOH 5% cellulose and 2% activatedcarbon; 9) 0% NaOH, 5% cellulose and 5% activated carbon; 10) 0% NaOH,0% cellulose and 5% activated carbon; 11) 7% NaOH, 0% cellulose and 5%activated carbon; 12) 0% NaOH 0% cellulose and 5% activated carbon.

For the preparation of mixtures 1 to 8 solutions and alkalinedispersions of cellulose were initially prepared. First, the sodiumhydroxide was solubilized in water and the solution was cooled to 0° C.using an ice bath. The cellulose was added to the NaOH solution and themixture was homogenized in a disperser at 6500 rpm for 5 min and at 0°C. The mixture was kept at −20° C. in a freezer for 2 h. Afterpreparation of the solutions and cellulose dispersions, the mixtures 1to 8 received additions of commercial activated carbon resulting in theconcentrations listed above. The mixtures 9 to 12 were prepared byadding the components to water. All mixtures were made in plasticcentrifuge tubes and shaken in a reciprocal motion shaker at 360oscillations per minute with a displacement of 2 cm for 15 h. Themixtures remained static for 24 h at room temperature (24° C) and werephotographed after the decantation period.

The systems 9 and 10 show that carbon does not disperse in water withoutthe presence of cellulose, and much of the material remained in contactwith the hydrophobic wall of the vial, so it did not get hydrophiliccharacter, which should have been provided by adsorption of thecellulose.

In contrast, systems 1 to 4 show sedimentation of the carbon in thepresence of cellulose, with no carbon spread on the surface of theplastic bottle, such as the systems 9 and 10. The systems 1 to 4 showthe accumulation of the aggregate material only in a few regions of thevial, indicating that most of the carbon became hydrophilic due tocontact with the cellulose. Furthermore, no macroscopic separation ofthe constituents, cellulose and carbon, in the sediments was observeddespite the density difference of these compounds, showing the chemicalcompatibility between them.

The mixtures 5 to 8 present dispersions which remain stable after 24hours, the solids remain in suspension, without the formation ofmacroscopic domains of each species. These systems show that cellulosedisperses carbon in water.

FIG. 5 shows the flowchart of the process used in Example 1. The firststep is the preparation of an alkaline solution by addition of sodiumhydroxide in water, followed by cooling of this solution on an ice bath.Then, microcrystalline cotton cellulose was added to the NaOH and themixture homogenized in a disperser at 6500 rpm for 5 mitt at The systemwas maintained at −20° C. for 2 h, obtaining a solution containing 5%(w/w) of cellulose and 7% (w/w) of NaOH. The alkaline cellulose solutionwas warmed until the room temperature (24° C.) and commercial graphitepowder was added at a concentration of 2% (w/w). After the addition, themixture was stirred in a homogenizer with a reciprocal movement of 360oscillations per minute and a displacement of 2 cm for 15 hours.

DESCRIPTION OF THE INVENTION

Graphite is a material used in various applications as a lubricant,pigment and conductor of electricity and heat, it is highly hydrophobic,what makes its use in aqueous media difficult, in Which it can bedispersed using dispersing agents well-known in the area, such assurfactants and water soluble polymers. The importance of graphiteincreased very recently When it was discovered the possibility of itsexfoliation producing graphene lamellas, of monoatomic thickness.Graphene is, in the present, the most investigated material by materialresearchers and also of several technology areas that can be benefitedby its exceptional chemical, mechanical, electrical and opticalproperties. Amorphous carbons are materials very common in nature,easily obtained by incomplete combustion and pyrolisis processes. Theyhave great structural affinity with graphite and graphene but they arechemically more complex, due to the oxidation degree, highly variable.Its structure is much less regular than that of graphene and graphite,although polynuclear aromatic domains are prevalent.

Many applications of graphene, graphite and amorphous carbon require itsprior dispersion in water. For example, inks and conductive adhesivesformulated in aqueous medium require these compounds finely dispersedand stable in the medium. The amorphous carbons, specifically, arewidely used as adsorbents of contaminants soluble in water destinatedfor municipal supply, and in this function it would be very desirable tobe able to disperse in water the powdered carbon, what is hampered byits hydrophobicity, as in the case of graphene and graphite.

Given the importance of these materials and especially their aqueousdispersions, many researchers have made considerable efforts to obtainsuch dispersions. A proof of this is that the United States Patent TradeOffice (USPTO) registers 700 patents, searched combining the keywords“graphene” and “cellulose”. But when are searched “(graphene orgraphite) and cellulose” was founded 18.495 patents. Moreover, thenumber of patent applications filed since 2001 was 2.072 only searchedcombining keywords “graphene” and “cellulose”. These patents cover alarge number of specific applications in the areas of energy (solarcells, lithium batteries and others), lighting (LEDs), informationtechnology (printed and flexible electronic circuits), sensors,diagnostics and analysis devices, electrodes for industrial processes,structural materials for engineering and construction, among others.

The scientific publications also provide abundant evidence of the greatinterest by these materials. For example, an article that describes thedispersion of graphene in water (Li, D., Muller, M. B., Gilje, S.,Kaner, & R. B. Wallace G. G.; Processable aqueous dispersions ofgraphene nanosheets. Nature NanoTechnology, v. 3(2), p. 101-102, 2008)with more than 4.500 citations.

The methods used in the art to obtain aqueous dispersions of graphene,graphite and amorphous carbons are based on the use of surfactants andwater-soluble polymers as dispersants. Very popular methods such as thedescribed by Wallace, G. G. et al. (cited in [0037]) use a previous stepof oxidation of graphene forming graphene oxide which is easilydispersed in water. Unfortunately, the oxidation affects many of thedesirable properties of graphene, which can be partially recovered bythe reduction of the oxide in the presence of stabilizers to preventtheir reaggregation and precipitation from the dispersion.

The almost absolute prevalence of methods for graphene dispersion basedon the formation and subsequent reduction of graphene oxide becomesapparent when it was found few patents and publications by eliminatingof the words “graphene oxide” in the search. A search by eliminating ofthese words showed only six articles and a patent. The articles are:High Concentration and Stable Aqueous Dispersion of Graphene Stabilizedby the New Amphiphilic Copolymer; Wu, Shengli; Shi Tiejun; Zhang,Liyuan. Fullerenes Nanotubes and Carbon Nanostructures, v. 23, p.974-984, 2015; Liposome-induced exfoliation of graphite to few-layergraphene dispersion with antibacterial activity; Zappacosta, R.; DiGiulio, M.; Ettorre, V.; et al.; Journal of Materials Chemistry B, v. 3,p. 6520-6527, 2015; Aqueous graphene dispersions-optical properties andstimuli-responsive phase transfer; Ager, David; Vasantha, Vivek Arjunan;Crombez, Rene; et al., ACS NANO, v. 8, p. 11191-11205, 2014.;Interfacial engineering of polypropylene/graphene nanocomposites:Improvement of graphene dispersion by using tryptophan as a stabilizer”;You, Feng; Wang, Dongrui; Li Xinxin; et al., RSC Advances, v. 4, p.8799-8807, 2014; Preparation of PYP-PVA-exfoliated graphite compositecross-linked hydrogels for the incorporation of small tin nanoparticles;Delbecq, Frederic; Kono, Fumihiko; Kawai, Takeshi; European PolymerJournal, v. 49, p. 2654-2659, 2013; Role of poly (N-vinyl-2-pyrrolidone)stabilizer for the dispersion of graphene via hydrophobic interaction;Yoon, Seyoung; Journal of Materials Science, v. 46, p. 1316-1321; 2011.

The patent mentioned in [0039]above is: Lead-acid cell cathodelead-paste, comprehend lead powder, fiber, graphene liquid aqueousdispersion, acetylene black, barium sulfate, sulfuric acid and water,CN103367753, inventors Chen, T.; Gao, X; Huang, H; et al., ShandongUniversity. However, in this patent the graphene is chemically modified,which is one of the ways to make it hydrophilic.

Delbecq, Frederic; Kono, Fumihiko; Kawai, Takeshi; Preparation ofPVP-PVA-exfolied graphite cross-linked composite hydrogels for theincorporation of small tin nanoparticles. European Polymer Journal, v.49, p. 2654-2659, 2013; used only polyvinylpyrrolidone andpolyvinylalcohol as exfoliating of the graphite in aqueous medium, butwith low efficiency and very dilute solutions.

An unprecedented possibility of dispersion and stabilization ofgraphite, graphene and amorphous carbons in aqueous solution is the useof cellulose. This polymer, although abundant and well known in the art,presents some challenges to current knowledge, such as the problem ofinsolubility in practically all known liquids. Attempts to address thisproblem produced in the last 150 years, several products oftechnological importance such as rayon, cellophane, “artificial silk”,and more recently, regenerated cellulose fibers obtained from cellulosesolutions in N-oxide of N-methylmorpholine.

A recent possibility of solubilizing cellulose is the use of aqueoussolutions of NaOH at low temperatures or in the presence of urea,thiourea and some other hydrotropic additives. This possibility isinterpreted as evidence of the amphiphilic character of cellulose,hypothesis defended by the Swedish researcher Lindman, Bjorn (Alves, L.;Medronho, B.; Antunes, F. E.; Topgaard, D. and Lindman, Bjorn.Dissolution state of cellulose in aqueous systems. 1 Alkaline solvents,Cellulose, v. 23, p. 247-258, 2016) but that is not completely accepted.According to this hypothesis, the cellulose chains have hydrophilic andhydrophobic domains geometrically separated and the association betweenthe hydrophobic domains excludes the water contact with a significantpart of the chains area, causing its insolubility in water.

This invention exploits the possibility of connect hydrophobic domainsof cellulose chains with faces of graphene lamellas and surfaces ofparticles of graphite or amorphous carbon, leaving the hydrophiliccellulose domains in contact with the water, which should cause itsstabilization.

Researches familiar with the art, should not expect success this way forthe stabilization of graphene dispersions, graphite and amorphouscarbon, for several reasons: cellulose and graphite are known to beincompatible, even the cellulose is insoluble in water and itsamphiphilic nature is not recognized by most practitioners of the art.

However, the experiments described in the examples provided in thispatent show that the cellulose is, surprisingly, a dispersing andstabilizing of graphene, graphite and amorphous carbon. The cellulosecan be put in contact with the carbon allotropes in different ways: asalkaline aqueous solution of cellulose such as cellulose powder mixedwith graphite or amorphous carbon in dry conditions and as cellulosepowder mixed with graphite or carbon under water or another liquidcompatible with cellulose, graphite or carbon. In all cases, there is anassociation between cellulose and carbonaceous compound, characterizedby the impossibility of observing, by microscopic examination,separation of cellulose particles from the others, due to dispersion andstability in water of the carbonaceous compound and its rheologicalbehavior.

When graphite is dispersed with cellulose it is possible to exfoliategraphite forming graphene, depending on the relative amounts, theintensity of the contact between two reactants, the intensity ofmechanical action and the temperature. The graphene formed, when broughtinto contact with more cellulose, is also stabilized by it, so that thecellulose can be used to produce graphene stabilized, in an aqueousmedium.

The dispersions and slurries of carbon materials in this presentinvention comprise the use of cellulose (CAS Number 9004-34-6) or pulpcomposed mainly of cellulose (CAS Number 65996-61-4) dispersed partiallyor totally solubilized. The present invention comprises the use ofcellulose as a dispersing agent for materials formed mainly of carbonsuch as graphite, nanographite, graphene, amorphous carbons, colloidalcarbons, fullerenes and carbon nanotubes. The amounts of cellulosenecessary are conveniently expressed by the ratio of the masses ofcellulose and graphite or other carbonaceous material, and can vary from1 part of cellulose to 99 of graphite, nanographite, graphene, amorphouscarbon, colloidal carbon, fullerenes and carbon nanotubes and 60cellulose for 40 graphite, nanographite, graphene, amorphous carbon,colloidal carbon, fullerenes and carbon nanotubes.

The concentrations of graphite or other carbonaceous materials in liquiddispersions, slurry or dry mass may vary between 0.001% and 50% byweight of graphite on the weight of the dispersion.

The dispersions and slurries of this invention may be prepared inneutral or alkaline medium. Alkalis are selected from a group comprisingsodium, potassium, lithium, calcium and ammonium, tetramethylammonium,or aluminates and zincates of alkali and its concentration may varybetween 0% and 50% by weight.

In an alternative embodiment of the invention, the dispersion or slurrycan be produced with a neutralizing additive, such as sodiumbicarbonate, borax, boric acid or other substance with buffering actionat neutral pH. Neutralizing agents will be required to achieve thedesired pH, depending on the concentration of alkali used. The additivecan be added in solid form, in solution or in any other manner known inthe art, in any convenient concentration.

In another embodiment of the invention, the dispersion or solution ofcellulose in an alkaline medium is produced by addition of a hydrotropeadditive such as urea, thiourea, mono-, di- and triethanolamines,glycerol, ethanol and other alcohols, dimethylsulfoxide, toluenesulfonates, xylene sulfonates, cumen sulfonates, lignin sulphonates,benzoates, salicylates, citrates, acetates and other compounds known inthe art. The amounts of additives can vary between 0% and 25% by mass ofsolution or dispersion of graphite or other carbonaceous compound in thepresence cellulose.

In another embodiment of the invention, the alkaline cellulose solutionor dispersion is added with oxides of zinc, aluminum, vanadium, titaniunor germanium.

In another embodiment, the aqueous medium may be replaced partially orcompletely by a polar organic liquid, such as methanol, ethanol,iso-propanol, n-propanol, acetone, ethylene glycol, glycerol,mono-methyl ethylene glycol, containing or not an alkali, withconcentration ranging between 0 and 50%.

The following examples represent only some embodiments of the presentinvention and should not be considered, in any way, as limiting of thescope and inventive concept of the present invention, since there areadditional possible alternatives and arrangements.

EXAMPLES Example 1—Preparation of Aqueous Dispersion Containing 2% ofGraphite, 5% of Cellulose and 7% of NaOH

An alkaline solution was prepared by adding sodium hydroxide in waterand the solution was cooled to 0° C. in an ice bath. Microcrystallinecotton cellulose was added in NaOH solution and the mixture washomogenized in a disperser at 6500 rpm for 5 min and at 0° C. The systemwas kept at −20° C. for 2 h, obtaining a solution containing 5% (w/w)cellulose and 7% (w/w) NaOH. The alkaline cellulose solution was warmedto room temperature (24° C.) and commercial graphite was added at aconcentration of 2% (w/w). After the addition, the mixture was stirredin a disperser with reciprocal movement to 360 oscillations per minutewith a displacement of 2 cm for 15 hours.

The dispersion stability was evaluated by keeping the system standingfor 24 h. After this period, there was no settling of solids andappearance of the dispersion remained unchanged. Also, it was notobserved distinct domains of cellulose and graphite, indicating thatthere was no separation of the two species, despite the densitydifference (graphite from 2.09 to 2.23 g/cm³ and cellulose 1.5 g/cm³),showing the compatibility of the compounds.

The dispersion was centrifuged at 3000 rpm for 1 h at 20° C. and it wasobtained a sediment volume of 3.5 ml of a total volume of approximately5 mL. It was not observed heterogeneity in the sediment or itsseparation in graphite and cellulose.

Example 2—Preparation of Aqueous Dispersion Containing 5% of Graphite,5% of Cellulose and 7% of NaOH

An alkaline solution containing 5% of cellulose was prepared as inexample 1. The alkaline cellulose solution was warmed to roomtemperature (24° C.) and commercial graphite was added at aconcentration of 5% (m/m). The mixture was homogenized as in example 1,turning into a slurry.

The dispersion stability was evaluated by keeping the system standingfor 24 h. After this period, there was no settling of the solids, as inexample 1.

5 ml of the dispersion were centrifuged at 3000 rpm for 1 h at 20° C.,and it was obtained 3.6 ml of sediment volume.

Example 3—Preparation of Aqueous Dispersion Containing 2% of Graphite,5% of Cellulose and 1% of NaOH

A dispersion containing 5% (w/w) of cellulose and 1% (w/w) of NaOH wasprepared as in examples 1 and 2. The cellulose dispersion was warmed toroom temperature (24° C.) and commercial graphite was added at aconcentration of 2% (w/w). After the addition, the mixture was stirredas in examples 1 and 2.

The dispersion stability was evaluated by keeping the system standingfor 24 h. After this period, the solids were sedimented and a clearsupernatant was formed with no deposit of material on the wall of aplastic bottle, as occurred in the graphite dispersion in water. Thesedimentation of the particles indicates that graphite and cellulose arein contact and there are no macroscopic domains of both, andfurthermore, the solids remain in the aqueous medium, like awater-cellulose system.

5 ml of the dispersion was centrifuged at 3000 rpm for 1 h at 20° C.,and a sediment volume of 1.0 ml was obtained.

Example 4—Preparation of Aqueous Dispersion Containing 5% of ActivatedCarbon, 2% of Cellulose and 7% of NaOH

A solution containing 2% (w/w) cellulose and 7% (w/w) NaOH was preparedas in examples 1-3. The cellulose solution was warmed to roomtemperature (24° C.) and the activated carbon was added at aconcentration of 5% (m/m). After the addition, the mixture was stirredas in examples 1-3.

The dispersion stability was evaluated by keeping the system standingfor 24 h. After the period, there was no settling of solids, and thesystem remained unchanged. Also, it was not observed different domainsof cellulose and activated carbon, indicating that there was noseparation of the two species, despite the density difference (activatedcarbon 2.0 to 2.1 g/cm³ and cellulose 1.5 g/cm³), showing thecompatibility of compounds and, therefore, that the alkaline celluloseis a good dispersing of activated coal in water.

Example 5—Preparation of Aqueous Dispersion Containing 5% of ActivatedCoal, 5% of Cellulose and 1% of NaOH

A dispersion containing 5% (w/w) of cellulose and 1% (w/w) of NaOH wasprepared as in examples 1-4. The cellulose dispersion was warmed to roomtemperature (24° C.) and the activated carbon was added at aconcentration of 5% (m/m). After the addition, the mixture was stirredas in examples 1-4.

The dispersion stability was evaluated by keeping the system standingfor 24 h. After this period, the solids were sedimented forming a clearsupernatant without an uniform distribution of carbon in the wall of theplastic bottle, as observed in the activated carbon dispersion inaqueous NaOH solution. The sedimentation of the particles indicates thatthe activated carbon and cellulose are in close contact, because it wasnot observed macroscopic domains of both.

Example 6—Preparation of Aqueous Dispersion Containing 5% of ActivatedCoal, 5% of Cellulose and 7% of NaOH

A solution containing 5% (w/w) of cellulose and 7% (w/w) of NaOH wasprepared as in examples 1-5. The cellulose solution was warmed to roomtemperature (24° C.) and activated carbon was added at a concentrationof 5% (m/m). After the addition, the mixture was stirred as in examples1-5, turning it into a slurry.

The dispersion stability was evaluated by keeping the system standingfor 24 h. After the period, there was no settling of solids and thesystem remained unchanged. Also, it was not observed different domainsof cellulose and activated carbon indicating that there was noseparation of the two species, despite the density difference (activatedcoal 2.0 to 2.1 g/cm³ and cellulose 1.5 g/cm³), showing the chemicalcompatibility of the compounds, where the alkali cellulose is thedispersant of the activated carbon in water.

1-15. (canceled)
 16. A process for dispersion of graphite and graphenein a solution or dispersion of cellulose in alkaline aqueous medium, ata range of concentrations from 0.001% to 50% by weight, formingdispersed particles of graphene or graphite with nanometric thickness,the process characterized by the use of graphite or graphene powder,without the need to use oxidizing reagents or any other form of chemicalmodification of graphite or graphene.
 17. A process for spontaneousformation of dispersions of graphite and graphene in solutions ordispersions of cellulose in alkaline aqueous medium, at a range ofconcentrations from 0.001% to 50% by weight, the process characterizedby spontaneous swelling and dispersion of the graphite, since it isimmersed in the cellulose solution and gently stirred, periodically. 18.A process of dispersion of amorphous carbons in solutions or dispersionsof cellulose in alkaline aqueous medium, at a range of concentrationsfrom 0.001% to 50% by weight, characterized by the use of powderedcarbon, granulate carbon or any other known form of art, eliminating theuse of oxidizing reagents or any other chemical modification of carbon.19. A process for spontaneous formation of amorphous carbon dispersionsin solutions or dispersions of cellulose in alkaline aqueous medium, ata range of concentrations from 0.001% to 50% by weight, characterized byswelling and dispersion spontaneous of the powder or carbon grains,since they are immersed in the cellulose solution and gently shaken,periodically.
 20. A process for dispersion of others carbonaceousmaterials as carbon nanotubes, fullerenes and colloidal carbons insolutions or dispersions of cellulose in alkaline aqueous medium, at arange of concentrations from 0.001% to 50% by weight, formingdispersions of nanometric particles, eliminating the use of surfactantsor other dispersants.
 21. A process for spontaneous formation ofdispersions of other carbonaceous materials such as carbon nanotubes,fullerenes and colloidal carbons in solutions or dispersions ofcellulose in alkaline aqueous medium, characterized by spontaneousswelling and dispersion of the carbonaceous solids, since they areimmersed in the solution cellulose and gently shaken, periodically. 22.The process according to claim 16, whereas the mass ratio ranges betweenthe cellulose and the carbonaceous materials of 1 to 60 parts ofcellulose and between 99 to 40 parts of carbonaceous materials byweight.
 23. The process according to claim 22, whereas that cellulosecan be introduced into the process as solid powder or in an alkalinesolution or dispersion in water and the alkali concentration may varybetween 0 and 50% by weight of the dispersion or solution.
 24. A processfor simultaneous miscibilization of graphite or other carbonaceousmaterials such as carbon nanotubes, fullerenes and colloidal carbonsusing cellulose as dispersant, by mechanical mixing of the dried powdersproducing a powder mixture that can be dispersed in water without theneed for vigorous mechanical agitation.
 25. The process according toclaim 16, characterized by the dispersion of graphite or othercarbonaceous materials, such as carbon nanotubes, fullerenes andcolloidal carbons using cellulose as a dispersant, by mechanical mixingof the powders immersed in water, methanol, ethanol, iso-propanol,n-propanol, acetone, ethylene glycol, glycerol, mono-methyl ethyleneglycol, characterized by the production of stable dispersions orhomogeneous sediments, eliminating the use of vigorous mechanicalagitation.
 26. Electric conductive inks based on dispersions ofgraphene, graphite and other carbonaceous materials, such as carbonnanotubes, fullerenes and colloidal carbons using cellulose asdispersant, according to claim
 16. 27. Electric conductive adhesivesbased on slurries or dispersions of graphene, graphite and othercarbonaceous materials, such as carbon nanotubes, carbon fullerenes andcolloidal carbons using cellulose as dispersant, according to claim 16.28. A process of painting, printing and writing based on the use of inksaccording to claim
 26. 29. A process for production of solid films,coatings and poly-functional electric conductive adhesives and/orantistatic and radiation absorbers in the visible, ultraviolet andinfra-red based in the dispersions as described in claim
 16. 30. Aprocess for production of solid films, coatings and poly-functionalelectric conductive adhesives and/or antistatic and radiation absorbersin the visible, ultraviolet and infra-red based in the productsdescribed in the claim
 26. 30. A process for production of solid films,coatings and poly-functional electric conductive adhesives and/orantistatic and radiation absorbers in the visible, ultraviolet andinfra-red based in the products described in the claims
 27. 31. Aprocess for production of nanocomposites of graphene and othercarbonaceous materials, such as carbon nanotubes, carbon fullerenes andcolloidal carbons using cellulose as dispersant with other materials, inwhich cellulose is introduced previously or during the mixture of thecomponents of the nanocomposite.
 32. A process for production ofelectrodes for sensors, batteries, solar cells or industrial processes,which uses the nanocomposites described in claim
 31. 33. A process forproduction of electrodes for sensors, batteries, solar cells orindustrial processes, which uses the inks described in claim
 26. 34. Aprocess for production of electrodes for sensors, batteries, solar cellsor industrial processes, which uses the solid films, coatings andconductive adhesives described in claim
 27. 35. A process for productionof electrodes for sensors, batteries, solar cells or industrialprocesses, which uses solid films, coatings and conductive adhesivesdescribed in claim 28.